Conventionally as an LED element using a nitride semiconductor, a semiconductor layer structure (laminated semiconductor substrate) is formed by epitaxial growth on a sapphire substrate as represented by a blue light-emitting diode. Such a technique is disclosed, for example, in the following Patent Document 1 and Patent Document 2.
Patent Document 1 discloses an LED having a structure in which an n-type contact layer made of gallium nitride (GaN) as an n-type nitride semiconductor, an n-type cladding layer made of n-AlGaN, an active layer made of n-InGaN, a p-type cladding layer made of p-AlGaN, and a p-type contact layer made of p-GaN are sequentially laminated on a sapphire substrate. The active layer is achieved by a single-quantum well structure or a multi-quantum well
Further, a buffer layer made of GaN, AlGaN, or MN is formed between the sapphire substrate and the n-type contact layer. The n-InGaN that forms the active layer is doped with a donor impurity such as Si or Ge and/or an acceptor impurity such as Zn or Mg.
Patent Document 2 discloses contents with respect to a laminated semiconductor substrate that forms an LED in which, on AlN having a plane orientation aligned in the c-axis direction, a GaN layer having a lattice constant larger than AlN and having a plane orientation aligned in the c-axis direction is formed by growth, and further, an n-AlGaN layer having a lattice constant smaller than the GaN layer, an active layer having a multi-quantum well structure, and a p-AlGaN layer are sequentially formed thereon.